PHILADELPHIA -- It is hard enough to fix a secondary in six months, as the Eagles have proven the hard way. It is impossible to fix one in the three days between Sunday's 33-30 loss to San Diego and Thursday night's matchup with Alex Smith and Dwayne Bowe of the Kansas City Chiefs.

Cornerback Roc Carmichael, signed Wednesday from the Houston Texans practice squad, isn't going to cover Bowe. He'll be inactive for this game. But the move adds to a pool of young defensive backs the Eagles hope will be able to contribute as the season goes on.

The Eagles will get starter Bradley Fletcher (concussion) back after one week. But Brandon Hughes is injured again. After breaking his hand in training camp, Hughes returned Sunday and pulled a hamstring. The Eagles placed him on short-term injured reserve to make room on the roster for Carmichael.

"We've had concerns since we got here with depth at the cornerback spot," head coach Chip Kelly said. "So that is a big concern for us overall. Didn't have Brandon in the first game, didn't have Fletch in the last game, and now Brandon's out again."

Carmichael, 25, was a fourth-round draft choice by the Texans in 2011. He played in six games last season, but was released at the end of training camp. There was a report the Eagles were interested in claiming him, but that never happened and he signed with Houston's practice squad.

He joins seventh-round pick Jordan Poyer and waiver-wire pickup Shaun Prater in development. Poyer was pressed into service in both games because of injury to other corners. He was immediately targeted for a touchdown pass by Washington's Robert Griffin III. Prater has been inactive in both games as he gets a crash course in Bill Davis' defensive playbook.

"He's coming along," Kelly said. "We picked him up after the cut down to 53, so I know those guys are working very hard with him. Shaun’s working very hard himself. So we're hoping to get a chance to get him acclimated. But it's also not fair to him to throw him in the field if he doesn't understand what we're doing and expect him to make a play on a Thursday night or Sunday and turn around and say we haven't had a chance to cover that. But Shaun's coming, and we hope to have a chance to get him involved here soon."

The Eagles have the second-worst pass defense in the NFL and were helpless against San Diego's Philip Rivers on Sunday. Over the next three weeks, they face Smith, Peyton Manning and Eli Manning.